This 5 year career development award will provide the candidate with training in mixed research methods and their applications to understanding substance use and migration impacts on HIV and blood borne infections (BBIs) in minority and vulnerable populations. The new qualitative and mixed-methods training coupled with a Ph.D. in public health and prior health services research will prepare the candidate for independent, policy oriented research on complex social and migration factors in HIV prevention in minority and disadvantaged communities. The proposed career and training goals employ didactic and mentored learning to: (1) Develop a thorough understanding of social and environmental factors that contribute to substance use and facilitate transmission of BBIs in migrants; (2) Acquire expertise in developing and implementing mixed-methods protocols (i.e., qualitative and quantitative methods) to study substance use issues; (3) Obtain ongoing training in the ethical conduct in research, especially vis--vis vulnerable populations; (4) Develop the skills necessary for a successful academic research career (e.g., publishing peer reviewed papers, presenting at professional meetings, grantsmanship); and (5) Acquire an in-depth understanding of theory-based interventions that may reduce transmission of BBIs among migrant injection drug users (IDUs). A key aspect of this training involves investigating the influence of migration on risky substance use and sexual behaviors among migrant female sex workers who inject drugs (FSW-IDUs) in Tijuana, a city on the U.S.-Mexico border. The prevalence of HIV in FSW-IDUs is 12.3% This study uses a mixed-methods approach to (1) characterize prior and future migration decisions and resources of FSW- IDUs in Tijuana; (2) Describe the influence of community and family migration experiences on FSW-IDUs' decisions to engage in sex work and substance use behaviors, and (3) Examine the relationship between migration factors and engagement in risky sex and substance use behaviors. Data generated from this study will be used by the applicant to develop an R01 or R34 targeting migrant FSW-IDUs and HIV risks in the U.S.-Mexico border region. RELEVANCE (See instnjections): The public health relevance of this study lies in the study population's role as a bridge population, meaning that sexually transmitted infections or other BBIs may become generalized through engagement in risky sex and substance use behaviors by FSw-IDUs and their clients to other populations residing in the U.S.-Mexico border region as well as tourists to the region.